This project represents a continuation of series of collaborative studies performed to better characterize and understand immune deficiency. Mutations involving the genes for the common gamma chain (X-SCID) and Fas (ALPS) were being evaluated using Sanger sequencing techniques of genomic DNA with fluorescent probes. These studies have continued to identify a number of new mutations in both diseases and these data have been entered into the NIH NHGRI web site supporting each of these two disorders. This was followed by the inclusion of mutation analysis of patients with hyper IgM syndrome directed at the genes encoding CD40L and NEMO followed by sequencing for immune deficiency associated mutations focused on host defense defects with recurrent infections involving opportunistic intracellular organisms including genes encoding the interferon gamma receptor 1 and 2, the IL-12P40 and IL-12 receptor beta 1 genes. Finally, new additional genes have been added to the repertoire including genes encoding: AIRE, ARTEMIS, BTK, FOXP3, ICOS, IL-7R alpha, JAK3, mu heavy chain,SAP, WASp. That initial work is now complemented by NextGen sequencing studies evaluating panels of genes or whole exome sequencing (WES) using the Ion Torrent platform, and more recently the Illumina platform. This approach allowed us to screen patients referred to the NIH and on clinical research protocols with suspected primary immunodeficiency disorders. To date this approach allowed us to contributed to the identification and further identification of patients with novel and previously known primary immunodeficiency defects that were further confirmed by Sanger sequencing and functional testing. Our experience to date suggests that this is a cost effective approach for screening referred patients with clear evidence of defects in host defense and that resequencing using the standard Sanger method under defined circumstances may not be necessary in the future.